This invention relates to the art of powder metallurgy and more particularly to the method of making a high density powdered metal titanium alloy article and to the products of such method.
For many years, powder metallurgists have been attempting to produce structural powder metal alloys, such as titanium base alloys, which have physical properties approaching or equaling those of cast or wrought alloys of similar compositions. To accomplish this, various techniques have been developed to reduce the porosity of the powder alloys to a minimum to thereby increase the sintered density of the concerned article to near theoretical. These high densities result in strengths nearly equal to those of cast or wrought materials and at the same time reduce to a minimum the notch sensitivity of the resultant article due to retained porosity.
For example, it has been known in the prior art to produce powdered metal products with densities similar to those of wrought products by the use of secondary processing techniques such as hot or cold working and/or hot isostatic pressing. These secondary operations, however, greatly add to the cost of the finished product and are to be avoided, if possible.
In addition, it is known in the art to produce relatively high density powdered products by sintering them at a temperature which introduces a liquid phase. Much of the recent work in this area has involved introducing a transient liquid phase. However, the use of a liquid phase has the drawback of introducing many reliability problems, especially with regard to brittleness. Additionally, the control of the exact sintering temperature becomes very important and in commercial practice is very difficult to maintain.
Also, it is known in the art to produce relatively high density powdered products by forming them entirely out of a very fine grain powder. This technique, as evidenced by U.S. Pat. No. 3,744,993, requires extra processing steps to produce the fine powder and to assure that all the powder is of the proper size. However, this technique is not without significant problems. In this regard, perhaps the most significant problem associated with the technique of using all fine powder is that the smaller the particle size of the powder, the greater is its tendency to be pyrophoric. Obviously, it is desirable to avoid or minimize problems associated with the use of such pyrophoric materials.
Accordingly, it is the principal object of the present invention to provide a method of producing a powdered titanium alloy article by powder metallurgy techniques which article exhibits physical properties similar to those of an article formed from wrought titanium alloy of the same composition.
It is another object of the present invention to provide an improved method of producing high density titanium alloys from powders by means of a single pressing and sintering operation.
It is still another object of the present invention to provide an improved powdered metal high density article.
A further object of the invention is to provide a powder metallurgy technique for producing a sintered titanium alloy having a density near theoretical while reducing the amount of fine particles required to produce the same to thereby minimize the problems typically associated with the handling of pyrophoric materials.
Other objects of the invention will become apparent from a reading of the following specification and claims.